Chemically treating wastewater to reduce contaminants is used in many industrial processes to allow reuse of wastewater, and to ensure that wastewater discharge meets required environmental quality standards. The type of treatment employed depends on the wastewater source, the type of contaminants in the wastewater, and the intended use of the treated water. Wastewater often contains suspended solids comprising particles finer than about 0.1 μm, which are not only difficult to filter out, but tend to remain in suspension indefinitely due to the repelling effects of electrostatic charges between the particles. To reduce the amount of fine particle contamination, or turbidity of the water, treatment systems typically introduce coagulating and/or flocculating agents into the wastewater. The coagulating agent neutralizes the electrostatic charges on the particles, which allows the particles to come into contact with each other and form larger particles. The flocculant may accelerate the agglomeration process by causing colloids and other suspended particles in the wastewater to aggregate, thereby forming large particles commonly referred to as floc particles or floc. The floc may then be removed from the treated water by, for example, sedimentation and/or floatation.
Coagulating and flocculating agents are typically added to wastewater in a mixing or reaction tank. Additional chemicals, such as acids or bases that are added to adjust the pH of the water to improve the effectiveness of the coagulant, or chemicals that react with and neutralize other contaminants, may also be added at this stage. The amount of the agents that must be added depends on the level of contamination and the volume of water being treated. For example, if too little of the coagulating agent is added, the turbidity of the wastewater may not be sufficiently reduced. On the other hand, adding excessive amounts of chemicals to the wastewater results in wasted chemicals, and can also result in the agents themselves becoming unwanted contaminants in the treated effluent.
To determine if sufficient chemical treatment agents are being added to the wastewater, samples of the treated wastewater may be taken and analyzed by measuring turbidity, pH, and/or chemical content. Typically, the wastewater samples must be allowed to settle before measuring turbidity so that the floc particles do not interfere with the measurement. For this reason, samples are typically taken after the sedimentation and/or floatation stages of treatment. However, water samples obtained at this stage of treatment may reflect chemical levels from hours earlier. Thus, by the time an increase in turbidity or the chemical content of the wastewater is detected, the amount of treatment agents present in the reaction tank may have drifted significantly away from their optimum level. In addition, because the contamination level of the inflowing wastewater may change over time, the measurements of samples that reflect wastewater introduced into the reaction tank hours earlier may not provide an accurate indication of how much treatment agent needs to be added to the reaction tank at the present time. The sedimentation or flotation effluent sample measurement may thereby provide an inaccurate indication of how much of a treatment chemical needs to be added to the incoming wastewater.
Consequently, there is a need for improved systems and methods for determining the turbidity of wastewater, as well as the optimum amount of chemicals to add to wastewater in a wastewater treatment system.